Color in Gemstones

[zeolite]

Gems & Gemology is a leading journal of accurate scientific information on gemstones. The three most important issues in the 30+ year history of this journal were “an update to color in gems”:

Volume XXIII, Fall 1987, pages 126-139, “Introduction and colors caused by dispersed metal ions”

Volume XXIV, Spring 1988, pages 3-15, “Colors involving multiple atoms and color centers”

Volume XXIV, Summer 1988, pages 81-102, “Colors caused by band gaps and physical phenomena”

Since my collection of Gems & Gemology is second only to GIA, I will quote sections of these difficult to find, older issues.

This post is in response to another thread on alexandrite w/vanadium. I will not take sides or discuss fluorescence. I will just quote sections concerning alexandrite, chromium, vanadium, and other color change stones.

Fall 1987, page 138, table 1 (dispersed metal ions and the colors they cause in various gem materials)

V3+ octahedral color-change effect: corundum and some rare pyropes and pyrope-spessartine
(my comment: V3+ means tri-valent vanadium in octahedral crystal coordination)

Cr3+ octahedral color-change effect: chrysoberyl/alexandrite: some pyropes
(my comment: Cr3+ means tri-valent chromium in octahedral crystal coordination)

Spring 1988 page 31 Chrysoberyl and Alexandrite from the Pegmatite Districts of Minas Gerais, Brazil

The Hematita alexandrites contain 0.30-0.44 wt % Cr2O3, 1.11-1.59 wt % Fe2O3, and 0.01-0.03 wt % V2O3

Summer 1988, page 95, table 4 (causes of color on most gem materials)

Color change (alexandrite) Cr3+ in octahedral coordination
Color change (corundum) Cr3+ and/or V3+ in octrahedral coordination in a particular range of concentration

 

[LD]

Mr Zeolite - I would just like to add a link to the thread you contributed to when we discussed vanadium (in chrysoberyls) in general:


[URL='https://www.pricescope.com/community/threads/strange-stone-vanadium-chrysoberyl.140166/page-2?hilit=vanadium']https://www.pricescope.com/community/threads/strange-stone-vanadium-chrysoberyl.140166/page-2?hilit=vanadium[/URL]

 

[Barrett]

Since steves thread is gone I am glad I did the ole copy/paste before I submitted this in his thread as I would hate to type it up again to post it here

Some varities of alexandrite show a fluorescence under long and shortwave light, where as the Cr-poor varities of chrysoberyl show no response. You don't see it to much due to the levels of iron which are generally higher than the Cr and most definitely with the V As much as 6 wt%(total weight Fe)(Zacek & Vrana 2002) Where as the Cr2O3 almost never tops 2 wt.%(total weight Cr)(Downes & Bevan 2002). As for Vanadium in alexandrite..many Hematita stones contain vanadium to some degree with very low iron.(Proctor 1988 G & G) Also alexandrite from Dowerin (Australia) contain large amounts of vanadium.(Downes & Bevan 2002)
All of this info from Daniel Marshall
Department of Earth Sciences
Simon Fraser University, BC Canada